A proposed solution to the problem of transfusion-associated viral hepatitis is the use of saline-washed packed red cells as the usual form of blood replacement. The present study seeks to determine whether the most widely used technique of washing red cells actually achieves a significant reduction in the incidence of transfusion-associated infections. Its method is a prospective comparison of risk among patients receiving only washed erythrocytes those given unprocessed units, and untransfused patients undergoing open-heart surgery. An additional goal is to determine the amount of dilution necessary to provide a virus-free product, if only for special purposes such as anti-Rh hyperimmunization, including the need to rid the material free of particles adherent to, or contained within, cellular elements other than erythrocytes.